sibilant vs spirant

sibilant and spirant both are nouns.

Word	Noun	Adjective	Verb	Adverb
sibilant	Yes	Yes	No	No
spirant	Yes	Yes	No	No

As adjectives, sibilant and spirant are synonyms defined as:

sibilant and spirant: of speech sounds produced by forcing air through a constricted passage (as `f', `s', `z', or `th' in both `thin' and `then')

Other synonyms of sibilant include continuant, fricative, strident.

As nouns, spirant is a hypernym of sibilant; that is, spirant is a word with a broader meaning than sibilant:

sibilant: a consonant characterized by a hissing sound (like s or sh)
spirant: a continuant consonant produced by breath moving against a narrowing of the vocal tract

Other hypernyms of sibilant include fricative, fricative consonant.

sibilant (noun)	spirant (noun)
a consonant characterized by a hissing sound (like s or sh)	a continuant consonant produced by breath moving against a narrowing of the vocal tract

sibilant (adjective)	spirant (adjective)
of speech sounds produced by forcing air through a constricted passage (as `f', `s', `z', or `th' in both `thin' and `then')	of speech sounds produced by forcing air through a constricted passage (as `f', `s', `z', or `th' in both `thin' and `then')